Present apparatus and methods for delivering power to active heart-failure treatment devices or non-cardiac devices with similar energy requirements may be problematic. For example, power conduits comprised of wires and tubes penetrating the skin may become infected. Similarly, trans-integumental transformers may present the risk of power-draining electromagnetic cross-coupling. Neither nuclear nor chemical batteries have proven to be effective for powering quantities beyond those of pacemakers and defibrillators. Likewise, power supply limitations and issues limit the practicality of various non-cardiac devices as well.
To address these limitations, the linear harnessing of contractile power from multiple in situ skeletal muscles has been investigated. Under this approach, underutilized, nonessential skeletal muscles are left in their natural sites, where they are conditioned to fatigue resistance and paced using techniques first developed in the cardiomyoplasty field. The tendon or distal muscle is connected to a hydraulic or other type of energy converter rather than to its natural insertion member, such as a bone.
Examples of specific muscles that have been harnessed in accordance with the principles described above include the psoas major, pectoralis major, latissimus dorsi, rectus abdominis, and one or more heads of the quadratus femoris muscles. These muscles have been shown to reliably and repetitively produce displacements in the range of about 10 to about 25 mm at mean contractile forces of about 10 to about 50 N, thereby yielding stroke work in the range of about 100 to about 1250 N-mm (equivalent to about 0.1 to about 1.25 Joules) per individual muscle. Ten percent of this energy may be recouped elastically and briefly stored for pre-stretch (preloading) to improve efficiency for subsequent beats. Assuming transmission efficiency losses of about 50% and rates in the range of about 25 to about 30 contractions per minute per muscle, harnessing of, for example, 2 to 6 muscles, may produce sufficient power for full circulatory power requirements (1 to 1.5 W). These values are averaged both over time and population. However, time-varying alterations and individual differences in energy potential may parallel similar differences in energy requirements. Thus, while circulatory power requirements may be greater during brief intervals of time (e.g., during heavy exercise), skeletal muscle potential may also be greater during the same time intervals. Similarly, both circulatory power requirements and nonessential skeletal muscle power potential may generally vary with body size and may be greater or lesser than the estimated average population values described above.
Linear harnessing of multiple in situ skeletal muscles, requires at least four technical capabilities. Linear harnessing may require, for example, approaches to effectively pace skeletal muscles for indefinite periods as well as methods to transform both muscle biochemistry and performance from anaerobic to aerobic, i.e., from quick bursts during exercise to the lower powered but non-fatiguing behavior most commonly seen in the flight muscles of birds. Similarly, linear harnessing of multiple in situ skeletal muscles may require methods of coupling muscles or their tendons to non-living (prosthetic) mechanical members capable of durable force transmission and methods of transferring the power so harvested to an active circulatory support device such as a total artificial heart, a ventricular assist device, a counterpulsator, or other like devices.
The required methods of coupling muscles or their tendons to non-living mechanical members capable of durable force transmission have been taught, for example, by U.S. Pat. Nos. 6,214,047 and 6,733,510 both issued to Melvin. The requirement of methods of transferring the power to an active circulatory support device, however, has not been demonstrated to be reliable over extended time periods notwithstanding, for example, the teachings of hydraulic systems in U.S. Pat. No. 5,888,186 to Trumble, U.S. Pat. No. 5,718,248 to Magovern and U.S. Pat. Nos. 5,984,857; 5,701,919; 5,653,676; and 5,344,385, all assigned to Thoratec, Inc.
The limitations of these devices taught in the prior art (referenced above) lie in the imposed movement of discrete parts through tissue required by their respective operations, which may result in an increased potential for scarring tissue which may tend to immobilize and limit motion. These devices are also limited by their physical bulk and by the potential of hydraulic seals to fail in their welded metal bellows or piston mechanisms.